package cn.icatw.leetcode.editor.cn;
//编写一个程序，通过填充空格来解决数独问题。
//
// 数独的解法需 遵循如下规则：
//
//
// 数字 1-9 在每一行只能出现一次。
// 数字 1-9 在每一列只能出现一次。
// 数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）
//
//
// 数独部分空格内已填入了数字，空白格用 '.' 表示。
//
//
//
//
//
//
// 示例 1：
//
//
//输入：board = [["5","3",".",".","7",".",".",".","."],["6",".",".","1","9","5",".
//",".","."],[".","9","8",".",".",".",".","6","."],["8",".",".",".","6",".",".",".
//","3"],["4",".",".","8",".","3",".",".","1"],["7",".",".",".","2",".",".",".","6
//"],[".","6",".",".",".",".","2","8","."],[".",".",".","4","1","9",".",".","5"],[
//".",".",".",".","8",".",".","7","9"]]
//输出：[["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8
//"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],[
//"4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9",
//"6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4",
//"5","2","8","6","1","7","9"]]
//解释：输入的数独如上图所示，唯一有效的解决方案如下所示：
//
//
//
//
//
//
//
//
//
// 提示：
//
//
// board.length == 9
// board[i].length == 9
// board[i][j] 是一位数字或者 '.'
// 题目数据 保证 输入数独仅有一个解
//
//
// Related Topics 数组 哈希表 回溯 矩阵 👍 1844 👎 0


//Java：解数独
public class T37_SudokuSolver {
    public static void main(String[] args) {
        Solution solution = new T37_SudokuSolver().new Solution();
        // TO TEST
    }

    //leetcode submit region begin(Prohibit modification and deletion)
    class Solution {
        public void solveSudoku(char[][] board) {
            solve(board);
        }

        private boolean solve(char[][] board) {
            for (int row = 0; row < 9; row++) {
                for (int col = 0; col < 9; col++) {
                    if (board[row][col] == '.') {
                        for (char num = '1'; num <= '9'; num++) {
                            if (isValid(board, row, col, num)) {
                                board[row][col] = num;
                                if (solve(board)) {
                                    return true;
                                } else {
                                    board[row][col] = '.';
                                }
                            }
                        }
                        return false;
                    }
                }
            }
            return true;
        }

        private boolean isValid(char[][] board, int row, int col, char num) {
            for (int i = 0; i < 9; i++) {
                if (board[row][i] == num) return false; // check row
                if (board[i][col] == num) return false; // check column
                if (board[row / 3 * 3 + i / 3][col / 3 * 3 + i % 3] == num) return false; // check 3x3 block
            }
            return true;
        }
    }


//leetcode submit region end(Prohibit modification and deletion)

}
